1. Field of the Invention
This invention relates to the rotor control system of a helicopter, and in particular to such a system in which each rotor blade can be controlled individually and without a conventional swashplate.
2. Prior Art
The swashplate has been the heart of the helicopter control system from the inception of the helicopter and continues in a critical role even today. See, for example, U.S. Pat. Nos. 1,909,845, 2,338,923, 2,494,209, 3,050,274, 3,841, 586, 3,972,491, 4,027,999, and 4,243,385.
The swashplate has served as probably the single most important component of the rotor control system for transferring both collective and cyclic control to the rotor. It is, of course, an essentially mechanical system which is subjected to a variety of loads, ranging from fatigue loads resulting from flight conditions to the loads associated with applying control to the rotor. Traditionally, the swashplate has been relatively heavy, a result of the often severe loading to which it is subjected. The structural integrity of the swashplate is crucial to the survivability of the helicopter, and consequently factors of safety needed to be high in designing the swashplate.
In recent years, composite materials have found greater application in the design of helicopters due to the ability which composite materials offer for load redundancy and weight savings. The major area of application for composite materials, however, has been in the upper rotor head. See, for example, U.S. Pat. Nos. 4,095,322, 4,247,255 and 4,316,701. The swashplate has somehow eluded the advance of composite materials, at least in most helicopters now flying. No doubt that the application of composite materials to helicopters will continue and reach the swashplate as well. Even so, the result will be less, in terms of weight at least, than a control system without a conventional swashplate.
Integration, i.e., the coordination of separate and diverse components into a more manageable system, is becoming evident in helicopter design. See, for example, U.S. Patent Nos. 3,080,002, 3,486,832 and 4,302,154. These patents disclose an integration of sorts in which the helicopter transmission is integrated with the rotor drive shaft and swashplate. Here again, the swashplate occupies a central role.